Urban GPS experience

It’s possible to use the GPS Map 60c in an old Marimekko bag in a mobile phone pocket just small enough that the aerial sticks out. In this way it can be placed in windows of buses or cars without it sliding around, and I can walk around without looking like a geek or getting mugged.

Problems

In short, GPS doesn’t work well in dense urban environments like most European cities. This is from the perspective of a pedestrian confined to the pavements (sidewalks) and public transport. From a few experiences whilst being driven around, it seems to work well in a car, probably because of the clear sky area available in the middle of the road. Inclement weather and green trees also seem to be problematic.

In these last few months, attempting to record a good quality database of tracks to geo-locate my photographs, I must have looked really odd. Face in device, stopping on street corners, stopping in the middle of street crossings and scrambling to grab the front seat of the bus. Discovering that GPS doesn’t just passively work is a great disappointment and my dataset is clouded with gaps and anomalies.

Some other observations

• Fast turns when using public transport or car result in wild deviations: re-aquiring satellites is the problem
• Need a road that aligns with at least 4 satellites to get an acceptable track, anything else and the errors can accumulate
• Glass buildings can result in ‘reflections’ of position, eg jumping to other locations due to reflected signals
• I sit on the outside or front of buses: to get a wider expanse of sky area: I am constantly aware of sky cover
• The relative position of satellites is beginning to have an effect on the side of the street that I walk on
• Walking in the middle of the street: had a couple of near misses with cars – the moving map is just too engaging
• I would like an explanation of the lost track calculations: this device seems to use the last-known bearing and velocity to guess new tracks when the signal fails. This is very unreliable and problematic as it fills the map with phantom trails
• The track can be more useful over time than the (base) map: it shows my personal space and personal routes, I know where I have been and can use it to retrace routes or places. Popular routes build up in blackness and thickness. Home area becomes an abstract scatter plot of routes, but it’s very familiar

• Stored waypoints are really useful for getting large, general bearings on location: zooming out and seeing a relationship to two known landmarks can be really useful in an unknown area